CH 302 1st Edition Lecture 9 Outline of Last Lecture I. Concept of Equilibrium ConcentrationsII. Law of Mass ActionIII. Equilibrium ConstantOutline of Current Lecture I. Equilibrium Constant, KII. Relationship between K and GIII. Equilibrium Response to ChangeCurrent LectureEquilibrium constant, K:1. Write the equilibrium constant expression for CaCO3 (s) CaO (s) + CO2 (g):K = PCO2(Because solids are not expressed in the equilibrium constant expression)2. Write the equilibrium constant expression for Ca(OH)2 (s) Ca 2+ (aq) + 2 OH- (aq)K = [Ca2+][OH-]^2(Remember that solids are not shown in the expression)3. Calculate Kc given Kp for N2 (g) + 3 H2 (g) 2 NH3 (g) Kp = (RT)^n KcN = 2 -4 (moles of gas)Kc = Kp (RT)^2 The relationship between K and G:- Pure products (in standard state) are lower in free energy- Equilibrium is achieved at minimum free energy - Delta G difference in molar free energy of products and reactants at any definite fixed composition of reactants and products- DG = DG° + RT ln Q at equilibrium- Q = activities of products divided by activities of reactants- Q is the reaction quotient (tells us where on the reactant path we are located)- Q = K, DG° = 0- DG = -RT ln K MEMORIZE THIS!o Therefore K depends on GEquilibria Response to Change:Le Chatelier’s Principle states that when a stress is applied to a system in dynamic equilibrium, the equilibrium tends to adjust to minimize the effect of the stress- Types of stress:o Adding or removing reagents When you add reactant, reaction shifts right When you remove product, reaction shifts right When you add product, reaction shifts lefto Changing volume of gas phase Compression: composition will change in a way that minimizes the resulting increase in pressure Expansion: composition will change in a way to increase the pressure Inert Gas: No effect on Q so no shift at constant volume When you increase pressure (compress), reaction moves towards side with fewer gas moleso Adding or removing heat Exothermic reactions, heat is like a product so when temperature increases, reaction shifts to the left Endothermic, temperature increases and k increases so heat is like a reactant and shifts to the
View Full Document
Unlocking...